Methane Density Research Articles

Microscopic scale influence of functional groups on the displacement behavior of coalbed methane by hot humid flue gas: A molecular simulation study based on the dynamic injection process

Building upon the CO2-ECBM technology (CO2-Enhanced Coaled Methane Recovery Technology), hot flue gas injection for displacing coalbed methane has been proposed to improve methane recovery efficiency and reduce the costs associated with CO2 capture during the displacement process as well as flue gas desulfurization and denitrification at coal-fired power plants. To explore the microscopic mechanisms of displacement and the influence of functional groups, this study used Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) methods with Materials Studio software to model slit pores grafted with various functional groups for gas adsorption simulations. The adsorption characteristics of eight key functional groups (-C=OCH₃, -COOH, -CH₂OH, Ar-OH, -OCH₃, -C6H6, -CH₃, -CH₂) for hot flue gas and methane were analyzed, focusing on adsorption strengths and underlying mechanisms. Simulations of the dynamic injection of hot flue gas were conducted, monitoring energy changes and methane density distribution to establish the relationship between adsorption strength and the difficulty of coalbed methane (CBM) displacement. The results indicate that in this simulation, the methane displacement efficiency using hot flue gas to displace coalbed methane exceeded 98%, demonstrating significantly better displacement performance compared to the use of pure carbon dioxide or nitrogen. Although both methane and hot flue gas show that greater interaction energy with pores makes displacement more difficult, the underlying causes differ. A comparison of the interaction energies between different functional groups and various gases reveals that oxygen-containing functional groups (-C=OCH3, -COOH, -CH2OH, Ar-OH, -OCH3) are unfavorable for the displacement of coalbed methane by wet hot flue gas, whereas aliphatic hydrocarbons (-CH3, -CH2) facilitate the displacement process.

Influence of Supercritical Conditions on Isothermal Adsorption Capacity Calculation of Methane and Model Optimization.

The study of isothermal adsorption models for coal and methane under supercritical conditions helps us to understand the gas content distribution in coal seams and improve gas management in coal mines. Coal samples from the Hebi mine and Longshan coal mine were selected for this research. Using the weight method, isothermal adsorption curves of supercritical methane at temperatures of 308, 313, and 318 K were measured. The adsorption phase density of supercritical methane was obtained by using the intercept method and model fitting, and the absolute adsorption capacity of methane was calculated. Simultaneously, the pore volume and specific surface area of the coal samples were tested, and the isothermal adsorption model for supercritical methane was studied and optimized. The results indicate that using mercury intrusion, low-temperature N2, and low-temperature CO2 adsorption methods for testing coal sample pore structures allows for multiscale characterization of the coal pore structure. Based on the Gibbs excess adsorption theory, the phase density of methane obtained from the intercept method and model fitting effectively represent the isothermal adsorption curve of supercritical methane. By combination of the specific surface area and pore volume distribution of the coal with the absolute adsorption capacity of methane, the number of methane adsorption layers on the coal surface was calculated to be between 1.11 and 1.3 layers. This suggests that the isothermal adsorption model for supercritical methane on coal is not solely micropore filling or single molecular layer adsorption but primarily single molecular layer adsorption with concurrent micropore filling adsorption. Based on this adsorption mechanism, an L-DA isothermal adsorption model for supercritical methane on coal was established. The L-DA isothermal model shows good fitting results and effectively explains the adsorption characteristics of supercritical methane on coal.

Research on the hazards of gas leakage and explosion in a full-scale residential building

The gas explosion in residential building has always been a highly concerned problem. Explosions in homogeneous mixtures have been extensively studied. However, mixtures are often inhomogeneous in the practical scenarios due to the differences in the densities of methane and air. In order to investigate the effects of gas explosions in inhomogeneous mixtures, experimental studies involving gas leakage and explosion are conducted in a full-scale residential building to reproduce the process of gas explosion. By fitting the dimensionless buoyancy as a function of dimensionless height and dimensionless time, a distribution model of gas in large-scale spaces is established, and the mechanism of inhomogeneous distribution of methane is also be revealed. Furthermore, the stratified reconstruction method (SRM) is introduced for efficiently setting up inhomogeneous concentration fields in FLACS. The simulation results highlight that for the internal overpressure, the distribution of methane has no effect on the first overpressure peak (ΔP1), while it significantly influences the subsequent overpressure peak (ΔP2), and the maximum difference between the overpressure of homogeneous and inhomogeneous distribution is 174.3%. Moreover, the initial concentration distribution also has a certain impact on the external overpressure.

Speed of sound in methane under conditions of planetary interiors

We present direct observations of acoustic waves in warm dense matter. We analyze wave-number- and energy-resolved x-ray spectra taken from warm dense methane created by laser heating a cryogenic liquid jet. X-ray diffraction and inelastic free-electron scattering yield sample conditions of 0.3±0.1 eV and 0.8±0.1 g/cm−3, corresponding to a pressure of ∼13 GPa. Inelastic x-ray scattering was used to observe the collective oscillations of the ions. With a highly improved energy resolution of ∼50 meV, we could clearly distinguish the Brillouin peaks from the quasielastic Rayleigh feature. Data at different wave numbers were utilized to derive a sound speed of 5.9±0.5 km/s, marking a high-temperature data point for methane and demonstrating consistency with Birch's law in this parameter regime. Published by the American Physical Society 2024

PLC BASED SCADA SYSTEM DESIGN FOR INSTANT MONITORING AND EARLY WARNING MECHANISM OF TOXIC GASES IN UNDERGROUND MINES

In this study, a real-time toxic gas measurement and early warning mechanism is proposed to prevent accidents that may occur in underground mining facilities. Temperature, oxygen (O2), hydrogen sulfide (H2S), methane (CH4), carbon monoxide (CO) and dust density sensor data are read via Arduino Mega analog inputs. All sensor data is transferred to the PLC-SCADA (Programmable Logic Controller - Supervisory Control and Data Acquisition) system via ethernet in real time. Thanks to the designed SCADA screen, sensor values can be monitored instantly. In addition, it can be checked whether the system is alarm and whether the ventilation system works. According to the underground coal mine regulations, work cannot be done in places where the mine air contains less than 19% oxygen, more than 2% methane, more than 50 ppm (0.005%) carbon monoxide and other hazardous gases. The highest permissible hydrogen sulfur ratio for 8 hours of operation is 20 ppm (0.002%). An early warning mechanism was created with the algorithm written taking these limits into consideration. The tests of the designed system were carried out in a laboratory environment and successful results were observed.

Theoretical analysis and numerical simulation of methane adsorption behavior on rough surfaces featuring fractal property

This work focuses on the control mechanism of adsorption behavior from rough surfaces featuring fractal property numerically. For that, we develop an equivalent characterization method for rough fractal surfaces, reproduce the adsorption process of methane on the surface by combining molecular dynamics and Grand canonical Monte Carlo (GCMC) simulations, analyze the control mechanisms of complex types of surface geometry on the methane adsorption process, and clarity the ratio of vertical roughness to horizontal complexity as key parameter to describe the adsorption capability. Our numerical results indicate that the adsorption density of methane in fractal and non-fractal slit pores varies with the fractal behavior of surface geometry, while the density of gas phase methane remains unaffected (all distributed around 0.06 g/cm3). And, the complexities of surface geometry process various effects on occurrence mode, adsorption potential energy (ɛ), and adsorption amounts. The surface original complexity will influence the force field, and alter the occurrence mode from monolayer adsorption to pore filling. Meanwhile, the width-to-depth ratio of surface original complexity has a negatively effects the ɛ of methane. The behavioral complexity of the surface reflects the number of small pores on it. For fractal slit pores, the maximum adsorption amounts are 2405.77, 2634.90, and 2749.46 mol/m3, respectively. They are smaller than that of the non-fractal slit pore, which is due to the increase of non-adsorption pores for the small diameter of pores. Above results give a clear explanation to the effects of fractal property on methane adsorption, which will provide a reference to study the adsorption process of methane in Coalbed Methane reservoir.

Molecular dynamic study of methane hydrate combustion-decomposition: Fluctuation-dissipation and nonequilibrium analysis

The combustion-decomposition of methane hydrate at micro-nano scale simulated by Reactive Force-Field molecular dynamics has characteristics of ultra-fast and nonequilibrium process. The normalized heat flux autocorrelation function of fluctuation at interface was introduced to study fluctuation-dissipation, which helped to clearly identify two distinct combustion-decomposition regimes dominated by sensible heat at burning boundary and latent heat at liquid-solid interface of decomposition. The highly synergistic rate of fluctuation period of heat flux between burning boundary and solid-liquid interface reaches up to 96.4 %. The localization characteristics and acoustic forms were observed based on the energy-spectrum of the heat flux at burning boundary and solid-liquid interface by Fourier transform. The energy-spectrum of heat flux at the two interfaces have peaks at 6 THz, and the energy-spectrum match well at lower frequency below ∼ 20 THz, justifying the highly synergistic rate. The curve of state density of methane is in good agreement with the spectral characteristics of interfacial heat flux. Finally, the mechanism of stable combustion of methane hydrate is simulated by interface adjustment and drainage, finding that continuous discharge of water from decomposed hydrate can maintain the rapid and stable combustion of methane, and the combustion rate of methane will increase by 5 times, and the number of various combustion production will increase significantly. The fluctuation period of various production meets that the later the production is generated, the shorter the fluctuation period. The fluctuation-dissipation mechanism gives deep light into the nonequilibrium process for the combustion-decomposition of methane hydrate at micro-nano scale.

Analysis of the influence of different pore ratios on methane adsorption characteristics of coal

The diverse pore structures in coal are pivotal in coalbed methane storage and transportation, making it highly significant to explore methane adsorption characteristics across varying pore sizes for effective prevention and control of coal mine gas disasters. Using the proposed graphene nanotube filling method, eight coal molecule models with varying pore size ratios were constructed, including four different pore radii: 0.35 nm, 0.55 nm, 0.75 nm, and 2 nm. Methane adsorption amount, methane density, and methane concentration distribution were obtained through Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The research results show that coal consisting of multiple pore sizes had a better methane adsorption capacity than a single pore size. Combining pore sizes of 0.35 nm, 0.55 nm, and 0.75 nm in a 1:2:1 ratio resulted in the highest excess methane adsorption capacity in coal, reaching 5.623 mmol/g. The single pore size of 0.55 nm in coal had the lowest excess adsorption amount of methane, which was 2.236 mmol/g. The presence of mesopores weakened the methane adsorption capacity of coal, and this weakening effect increased with the increase of mesopore proportion. In the model composed of single pore size micropores, the methane concentration inside the pores was uniformly distributed. The coexistence of multiple micropores may lead to methane filling in the micropores in a monolayer adsorption form. The coexistence of micropores and mesopores does not alter methane filling in the micropores and monolayer adsorption in the mesopores. The research results provide new insights into our understanding of the impact of pores on methane adsorption in coal.

Data-driven modeling to predict adsorption of hydrogen on shale kerogen: Implication for underground hydrogen storage

The interaction of hydrogen in shale gas formations holds significant interest for long-term subsurface hydrogen storage. Accurately and rapidly predicting hydrogen adsorption in these formations is crucial for assessing underground hydrogen storage potential. Many laboratory experiments and molecular simulations have been conducted to determine hydrogen adsorption. However, laboratory experiments and molecular simulations require complex setups and extensive calculations, which can be time-consuming. Consequently, end-users may prefer quick and accurate prediction of hydrogen adsorption to reduce the experimental and computational burden. This study introduces a novel model for predicting hydrogen adsorption using gradient boosting regression and available molecular simulation data from the literature. The data-driven model predicts hydrogen adsorption on kerogen structures based on pressure, temperature, adsorbed methane, hydrogen-to‑carbon ratio, oxygen-to‑carbon ratio, and kerogen density. We compared gradient-boosting regression with other machine learning tools, including artificial neural networks, symbolic regression assisted with genetic programming, decision trees, and random forests in terms of their capability to predict H2 adsorption on shale kerogen. A simple mathematical equation based on symbolic regression via genetic programming has also been provided, with training and testing coefficients of determination of 88.4% and 85.8%, respectively. However, the digital model created using gradient boosting regression outperformed all other machine learning tools, achieving a coefficient of determination of 99.6% for training data and 94.6% for testing data. A sensitivity analysis was also conducted that demonstrates the robustness of the developed model. In the case of kerogen type A, the order of increasing hydrogen adsorption is KIA < KIIA<KIIIA. Conversely, for kerogen type B, the trend is KIIA<KIIC<KIIB<KIID in terms of increasing hydrogen adsorption. This developed digital model offers higher prediction accuracy and finds applications in storing hydrogen in shale gas formations. The proposed model offers a substantial time-saving advantage in predicting hydrogen adsorption compared to laborious and time-consuming laboratory experiments and/or molecular simulations.

Flame Characteristics and Abnormal Combustion of Methane Port Injection and Isooctane Direct Injection with Injection Timings Considered

Natural gas (NG) is a low-carbon fuel that can achieve low carbon emissions and high efficiencies. However, the low mean molecular mass and low energy density of methane result in low engine performance, and blending methane with gasoline is an effective way of improving the performance of NG engines. In this study, flame characteristics (including abnormal combustion) and engine performance are optically studied under methane port injection and isooctane direct injection conditions. The results indicate that the addition of isooctane can significantly increase the power output of NG engines. Under partial-load conditions, the minimum ignition advance for best IMEP is delayed with the addition of isooctane because of the higher flame speed of isooctane, and isooctane addition primarily improves the turbulent flame propagation rather than the initial flame formation. As for the isooctane injection timing, the indicated mean effective pressure (IMEP) first increases and then decreases with the delay in isooctane injection. The hot spots in the flame images confirm that late injection results in isooctane inhomogeneity, which reduces the engine’s thermal efficiency. At high loads, the low energy density of methane can lower the knocking intensity, even in the presence of auto-ignition at a speed of 120.7 m/s. The knocking pressure can lead to the ejection of oil droplets, which can increase the flame speed in the subsequent cycle.

Methane adsorption of nanocomposite shale in the presence of water: Insights from molecular simulations

Accurately predicting gas adsorption in shale gas is essential for estimating production capacity and optimizing extraction processes. However, the complex nature of shale reservoirs (heterogeneous structure, organic–inorganic nanopores, moisture content, etc.) presents significant challenges in understanding the mechanism of methane adsorption. To address these challenges, a nanocomposite shale model incorporating kerogen and illite with slit pore widths of 1 nm, 2 nm, and 4 nm is created. The hybrid grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations are used to investigate methane adsorption in rigid and flexible shale models (kerogen matrix and clay mineral) at three different temperatures, several pressures, and various moisture contents. The simulation results show that the methane density distributions revealed asymmetrical behavior due to the heterogeneous surfaces. Factors such as kerogen flexibility, pore width, moisture content, temperature, and pressure were found to significantly influence fluid behavior. A comparative analysis between the rigid and flexible shale models, considering varying pore widths under both dry and moist conditions, revealed noteworthy differences. Kerogen's flexibility led to increased surface roughness and decreased adsorbed density. Conversely, the presence of water reduced methane adsorption sites in illite, resulting in diverse and complex behaviors dependent on pore widths in the shale model. Finally, the results suggest that using adsorbed volume instead of classical adsorption models is recommended for converting excess adsorption into absolute adsorption. This alternative approach can provide more accurate predictions and enhance the understanding of adsorption in shale gas systems.

The importance of pore-fracture connectivity in overmature marine shale for methane occurrence and transportation

Pore-fracture connectivity is a critical factor in gas occurrence and transportation in shale plays. To investigate the limiting factors of multiscale pore-fracture connectivity, which might control methane occurrence and transportation in shale reservoirs, small-angle neutron scattering (SANS) under vacuum and high-pressure conditions incorporated with repeated mercury intrusion capillary pressure (MICP), and field emission-scanning electron microscopy (FE-SEM) imaging after Wood's metal (WM) impregnation were performed on overmature marine shale samples of the Wufeng-Longmaxi and Niutitang Formations from south China. Based on the electron micrographs of the WM-injected samples, it was found that the sealing of the pore system by brittle minerals is the root cause for a reduction in overall pore connectivity within the shale matrix. Aside from being favorable to the preservation of organic and clay mineral pores, brittle minerals however, resulted in the closure of pore network, thus, forming an isolated pore system. The novel approach of integrating repeated MICP measurement and FE-SEM imaging after WM impregnation provides a new evaluation method for pore-fracture connectivity of shale. The minimum fraction of pores within the overmature shales accessible to methane was at 38% and 78% within 100 nm. Moreover, because of confinement effects, the density of methane in a pore space less than 20 nm under high pressure was greater than that of an ideal gas under the same pressure conditions which even increased with decreasing of pore size to several times of its inert state and formed nanoscale methane clusters. The combination of contrast-matching SANS (CM-SANS) and repeated MICP measurements can effectively reveal the connectivity of pores within the matrix and the connectivity between such pores and microfractures, which helps to evaluate the distribution of closed pores and dominant transport spaces of gas in shale reservoirs. Overall, the pore-fracture connectivity in overmature marine shale controls the amount of gas that is supplied from matrix pores into fracture systems and also affects the density of the gas in pore spaces within the matrix.

The Effects of Pore Wettability on the Adsorption and Flow Capacity of Shale Gas: New Insights from Molecular Dynamic Modeling

Pore wettability plays a key role in controlling shale gas adsorption and flow in marine shales. To reveal the mechanism of shale gas adsorption and flow in pores with different wettability (hydrophobic or hydrophilic), molecular modelling is simulated using the molecular dynamics method. Three pore assemblages, namely, the quartz–illite (Q–I) pores, the quartz–organic matter (Q–OM) pores, and the illite–organic matter (I–OM) pores, are proposed and the adsorption and diffusion behavior in these pores are simulated under different conditions. The results show that matrix compositions in shale greatly affect pore wettability. Water molecules preferentially absorb on the junction of materials and result in more hydrophilicity at the junction than pores. Methane density simulations reveal that free methane molecules form clusters in the Q–I pores, with higher free methane density than adsorbed methane. Methane molecules in the Q–OM pores are primarily adsorbed on organic matter. Free methane molecules extensively exist in the I–OM pores, leading stronger density of free methane than adsorbed methane. The more the proportion of free methane, the larger the methane self‐diffusion coefficient. This study provides new insights to understanding of shale gas adsorption and diffusion behavior, which is important for the effective development of shale gas reservoirs.

Investigations on Supercritical Methane Adsorption and Storage in the Lower Longmaxi Shale of Nanchuan Area, Southeast Sichuan Basin

A series of high-pressure methane adsorption measurements were performed at various temperatures on whole shale and kerogen samples collected from the Lower Longmaxi shale in the Nanchuan area, southeast Sichuan Basin, to investigate supercritical methane adsorption properties and evaluate in-place methane storage capacity as a function of burial depth. The results show that the supercritical Dubinin–Radushkevich (SDR) model fits the excess adsorption isotherms marginally better than the supercritical Langmuir model. However, the fitted adsorbed methane density of kerogens obtained from the SDR model may be greater than the liquid methane density at the atmospheric boiling point (0.423 g/cm3). The proposed multiple regression fitting carried out in this work illustrates that approximately 57.59% (34.51–85.45%) and 37.60% (10.74–59.52%) of the methane adsorption capacity at 333.15 K can be attributed to organic matter (OM) and clay minerals (CMs), respectively, for whole shales investigated. According to thermodynamic analyses, the significant contribution of OM to the methane adsorption capacity can be attributed to the stronger affinity between kerogens and methane molecules in contrast to that between CMs and whole shales. The methane storage capacity estimated as a function of burial depth showed that the adsorbed gas storage capacity declines with increasing burial depth between 2000 and 5000 m, while the free gas storage capacity shows the opposite trends. Gas accumulation pressure primarily exerts a significant effect on the free gas storage capacity rather than adsorbed gas storage capacity, and adsorbed gas storage capacity begins to exceed free gas storage capacity at shallow burial depths for normally pressured gas accumulations. Normally pressured shale gas accumulations at shallow burial depths, which are widely distributed in the residual syncline of the study area, should be given more attention due to their relatively low development costs and relatively high storage capacity for adsorbed gas.

The Pyrogeography of Methane Emissions from Seasonal Mosaic Burning Regimes in a West African Landscape

People have set fire to the savannas of West Africa for millennia, creating a pyrogeography. Fires render the landscape useful for many productive activities, but there is also a long history of efforts to regulate indigenous burning practices. Today, savanna fires are under scrutiny because they contribute to greenhouse gas emissions, especially methane. Policy efforts aimed at reducing emissions by shifting fire regimes earlier are untested. Most emissions estimates contain high levels of uncertainty because they are based on generalizations of diverse landscapes burned by complex fire regimes. To examine the importance of seasonality and other factors on methane emissions, we used an approach grounded in the practices of people who set fires. We conducted 107 experimental fires, collecting data for methane emissions and a suite of environmental variables. We sampled emissions using a portable gas analyzer, recording values for CO, CO2, and CH4. The fires were set both as head and backfires for three fire periods—the early, middle, and late dry season. We also set fires randomly to test whether the emissions differed from those set according to traditional practices. We found that methane emission factors and densities did not increase over the dry season but rather peaked mid-season due to higher winds and fuel moisture as well as green leaves on small trees. The findings demonstrate the complexity of emissions from fires and cast doubt on efforts to reduce emissions based on simplified characterizations of fire regimes and landscapes.

DYNAMICAL MODELING AND ANALYSIS OF METHANE EMISSION ABATEMENT

A nonlinear mathematical model is proposed and analyzed to study the effect of mitigation options on the control of methane emissions in the atmosphere caused by livestock and human populations so as to reduce global warming. Livestock population is one of the main agricultural sources of greenhouse gases in the world. It is assumed that the atmospheric concentration of methane increases in the atmosphere due to cumulative density of methane formed by various processes involved in the farming of livestock populations. Various human activities are also significant contributors to methane emissions. The most notable effects of global warming around the world include the progressive heating of the Earth’s surface, oceans and atmosphere; glacier melting; and various diseases. Mitigation options are applied to control the methane emissions considerably in the atmosphere caused by livestock and human populations which in turn reduces the effects of global warming. The data from model prediction is compared with actual methane data in the atmosphere and found to be fairly close.

Methane absorption of coal-measure shales with and without pore water from the Qinshui Basin, North China: Based on high-pressure methane absorption experiments

The coal-measure shale in the Qinshui Basin, North China has a high thermal maturity and a huge shale gas resource, but studies related to its gas-bearing property (GBP) are lack. In this paper, shale samples taken from the carboniferous coal-measure strata in the Yangquan block of Qinshui Basin were mainly investigated on their pore water contents and occurrence characteristics, and their high-pressure methane adsorption capacities under the dry and moist conditions. The results show that the pore water in the shale is in an ultra-low saturation state, occurring mainly in clay minerals (91% on average), significantly decreases its effective pore structure parameters, especially the nonmicropore specific surface areas (by 70.21% on average), and reduces its methane adsorption capacity (by 33% on average at 30 °C), with the adsorbed methane occurring mainly in micropores and controlled by the TOC content. The adsorption of methane on the shale is an exothermic process, and both the shale adsorption capacity and adsorbed methane density are reduced with increasing temperature. Pore water not only has a competitive adsorption with methane, but also weakens the adsorbed methane inter-molecular interaction forces, decreasing the methane adsorption capacity, especially under the low temperature and pressure conditions. The GBP models of a selected shale under the dry and moist conditions further indicate that pore water also decreases the adsorbed gas percentage to some extent, especially at a burial depth < 1500 m, and the adsorbed gas is dominant in the shale. These GBP characteristics of coal-measure shale should pay a great attention in the future exploration and development of shale gas in the Qinshui Basin.

МОДЕЛЬНО-ЭМПИРИЧЕСКИЙ РАСЧЕТ ПОТОКОВ МЕТАНА И ДИОКСИДА УГЛЕРОДА ИЗ ПОЧВ ТОРФЯНЫХ БОЛОТ

A new process-based model designed to develop a methodology for the inventory of green- house gas emissions from peatbog soils is presented. Within the framework of the general model, a new parameterized formula for calculating methane oxidation in the aerated soil layer and the vegetation layer is proposed. The proposed approach is defined as model-empirical, since the theoretical model relies on the use of values of model parameters determined by a specially developed experimental procedure. A detailed description of the model calibration by means of experimental studies of soil samples is given. Examples of the calculated dependences of methane and carbon dioxide flux densities on the peatbog water level are presented. A comparison with data on methane fluxes measured in boreal bogs demonstrated a satisfactory consistence of the calculated and measured values.

Variation of adsorption effects in coals with different particle sizes induced by differences in microscopic adhesion

The swelling strain caused by methane adsorption in coal affects reservoir permeability, further complicating the propagation of fluid pressure. The impact of different scales of pores in coal on the adsorption behavior was investigated by combining the reaction heat apparatus C80 and atomic force microscopy (AFM), followed by characterization of adsorption effect variation in coals with different particle sizes due to adhesion differences. The results show that the absolute adsorption volume (AAV) of the high-rank coal sample Chengzhuang (CZ) of 0.85–2.00 mm is 1.06 times higher than that of the medium-rank coal sample Qiyi (QY) under the pressure of 4.2 MPa. With the increase of pressure, more desorption occurs at different sites of adsorbed phase, resulting in the increase in the density of the free phase methane increasing the gap between AAV and excess adsorption volume (EAV). The larger the particle size of coal, the smaller the temperature variation during adsorption. In the AFM measurements, CZ containing 2026 adsorption pores exhibits stronger heterogeneity than QY, leading to the formation of more capillary condensation of methane. For the adsorption heat, methane tends to occupy sites with high adsorption potential at the beginning of adsorption to release large amounts of heat. Moreover, the adhesion force distribution of QY is more uniform than that of CZ, mainly concentrated between 1.5 and 3.0 nN. Subject to microscopic adhesion force, methane molecules in the effective adhesion region can be stably adsorbed to pores. Temperature affects the heterogeneity of adhesion, mainly the higher the temperature, the more concentrated the distribution of adhesion in coal. The findings contribute to the clarification of the adsorption kinetics of nanoscale carriers in coal reservoirs.

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